Conventional Nutrient Solution Research Articles

Nutrient Solution from Aqueous Extracts as an Alternative to Fertigation in Hydroponic

The reintegration of agro-waste into the same agriculture site fulfils the objective of the European Bio-Economy Strategy: to reduce transport costs, waste volume, and the need for mineral fertilizers. One of the fundamental principles in sustainable agriculture is the recycling of crop residues through composting or vermicomposting. From this process, it is possible to obtain organic matter for the production of aqueous extracts (tea) that can be used as a source of nutrients in fertigation as an alternative to mineral fertilizers. The objective of this research was to evaluate the use of an aerated or non-aerated aqueous extract as a recirculating nutrient solution in a hydroponic culture (NFT) of lettuce. For this, the test method was compared to hydroponic cultivation with a conventional nutrient solution. The conventional nutrient solution contained minerals or synthetic fertilizers and the aqueous extracts of vermicompost from vegetal residues of horticultural crops. The evolution of the chemical composition of the nutrient solutions during cultivation was analyzed, obtaining adequate concentrations of NO3−, K+, and Ca2+ and taking possible imbalances in nutrients such as P-H2PO4− into consideration. Plants fertigated with an organic and aerated nutrient solution obtained good yields and improvements in quality by having six times less N-NO3− in edible leaves compared to plants exposed to the mineral treatment. The preparation of aqueous extracts as a source of nutrients opens the door to circular agriculture to make processes in intensive production systems more efficient.

Development of Nutrient Solution Compositions for Paprika Cultivation in a Closed Coir Substrate Hydroponic System in Republic of Korea’s Winter Cropping Season

Other than in highland areas, the majority of paprika growers in Republic of Korea transplant during late summer and cultivate when temperatures are relatively low. Additionally, they typically apply European nutrient solutions and hydroponic technologies with different climates and cultivation periods. Therefore, this study was conducted to determine the optimal nutrient solution composition based on growth stages suitable for paprika (Capsicum annum L.) cultivation in closed hydroponic systems with a coir substrate during the winter cropping season. The nutrient solutions were supplied to all the paprika plants at pH 5.8–6.0 and electrical conductivity (EC) 2.0–3.5 dS·m−1 according to the target EC setting for each growth stage. The mixing ratio of the reused nutrient solution (drainage) to the fresh solution was maintained within 30% on an EC basis (0.6–1.1 dS∙m−1) at each irrigation event. Paprika plants ‘Cupra’ were grown in three different nutrient solutions using an automated fertilizer dosing system based on integrated solar radiation (ISR). Nutrient absorption patterns according to growth stages were investigated for each nutrient solution. To reduce the nutritional imbalances of major nutrients in the root zone (RZ, substrate), the nutrient solution ‘NIHHS (National Institute of Horticultural and Herbal Sciences)’ was adjusted considering the nutrition absorption patterns according to growth stages, ion balances between anions and cations, and differences between the ion concentrations in the RZ and with irrigation. NIHHS-Coir1 and NIHHS-Coir2 solutions with 5–10% and 10–15% readjustments of macronutrient concentrations in the NIHHS, respectively, were used to evaluate the suitabilities for cultivation and productivity, whilst the IKC (Informatie en Kennis Centrum) nutrient solution was used as the control. We investigated the influence of these solutions on growth, yield, and photosynthetic responses compared to the conventional nutrient solution. Throughout the entire cultivation period, the newly formulated NIHHS-Coir1 solution had a marketable fruit ratio (%) of 2.4–3.5% higher and a marketable yield (kg/m2) of 5.3–8.7% higher than those of the conventional IKC solution.

Treated domestic sewage as a nutrient source for strawberry under hydroponic cultivation

Purpose This study aimed to compare the hydroponic strawberry production using the conventional nutrient solution and treated domestic sewage, seeking fertilizer savings and identifying its nutritional status and physicochemical and microbiological attributes of fruits.Method The experiment was carried out in a greenhouse under the nutrient film technique (NTF) hydroponic system, with three treatments: DW – drinking water and chemical fertilizers, TDSS – treated domestic sewage supplemented with chemical fertilizers, and TDS– only treated domestic sewage. Each treatment consisted of four cultivation benches, a motor pump system, a timer, and a 500-L container to store nutrient solution. Four hydroponic profiles with a capacity for 12 plants were used on each bench, totaling 48 plants per bench and 192 plants per treatment. These benches were divided into four randomized blocks. We compared the nutrient content of treated domestic sewage to the conventional nutrient solution, amount of nutrients used in treatments, microbiological quality and quantitative and qualitative aspects of fruits, nutritional status of plants.Results The TDS treatment showed a significant difference compared to the others, with visual symptoms of nutritional imbalance in plants, lower productivity, and fruits more acid with a smaller diameter. Soluble solids content showed no statistical difference between treatments and the microbiological quality of fruits, which showed no presence of Escherichia coli.Conclusion The use of treated domestic sewage to compose the nutrient solution allowed obtaining savings of 33% in chemical fertilizers in the TDSS treatment compared to DW.

Hydroponic Lettuce Cultivation Using Organic Nutrient Solution from Aerobic Digested Aquacultural Sludge

The aim of this study was to demonstrate how aquacultural sludge can be processed and utilized as an organic nutrient solution (ONS) for hydroponic lettuce production. By using a previous developed method, approximately 80% of the processed sludge was reclaimed as a clear, nutrient-rich solution. The performance of the recovered nutrient solution on lettuce growth was assessed in a nutrient film hydroponic system. The results were compared to the results obtained using a conventional nutrient solution (CNS). Yield, fresh weight, water consumption, and nutrient and heavy metal content in leaf tissue were measured. In spite of a 16% lower average fresh weight obtained in ONS compared to the weight obtained in CNS, there was no statistical difference of the yield of lettuce among the two nutrient solutions. After the cultivation period, 90% of the lettuce heads grown in ONS exceeded the marked weight of 150 g. Foliar analysis revealed a similar or higher content of all nutrients, except of magnesium and molybdenum in the leaves of lettuce grown in the ONS compared to lettuce grown in the CNS. This study shows that nutrients recovered from aquacultural sludge can be utilized as fertilizer, thereby reducing the dependency on mineral fertilizer in hydroponic and aquaponic systems.

Effects of Hydrogen Peroxide on Organically Fertilized Hydroponic Lettuce (Lactuca sativa L.)

Hydroponic production typically uses conventional fertilizers, but information is lacking on the use of organic hydroponic fertilizers. Development of microbial communities and biofilm that can reduce dissolved oxygen availability is a difficulty with organic hydroponics. One potential solution is the use of hydrogen peroxide (H2O2) which can reduce microbial populations and decompose to form oxygen. However, information is lacking on the impact of hydrogen peroxide on hydroponic crop performance. The aim of this study was to determine the effects of H2O2 concentrations in deep water culture hydroponics by assessing how it affects plant size and yield in lettuce (Lactuca sativa L.) “Rouxai”. In this experiment, three H2O2 treatments, namely the application of 0, 37.5 or 75 mg/L H2O2 to 4 L aerated hydroponic containers with either conventional or organic fertilizer, were compared. The containers had either fish-based organic fertilizer (4-4-1, N-P2O5-K2O) or inorganic mineral based conventional nutrient solution (21-5-20, N-P2O5-K2O), both applied at 150 mg/L N. Three replicates of each H2O2 treatment–fertilizer combination were prepared resulting in a total of eighteen mini hydroponic containers each with one head of lettuce. There were two growth cycles: fall 2018 and spring 2019. When added to conventional fertilizers, both 37.5 mg/L and 75 mg/L of H2O2 led to stunted growth or death of lettuce plants. However, when 37.5 mg/L of H2O2 was applied to organic fertilizers, the lettuce yield nearly matched that of the conventionally fertilized control, demonstrating that the application of H2O2 has the potential to make organic hydroponic fertilization a more viable method in the future.

Respon Pertumbuhan Tanaman Pakcoy (Brassica rapa L) dengan Pemberian Teh Kompos Bulu Ayam pada Sistem Hidroponik

Wick system merupakan salah satu jenis hidroponik yang menggunakan sumbu sebagai media penyerap nutrisi. Teh kompos bulu ayam dapat dimanfaatkan sebagai pengganti nutrisi konvensional dalam budidaya tanaman pakcoy. Penelitian ini bertujuan untuk mengetahui pengaruh teh kompos bulu ayam dan menentukan nilai ppm terbaik pada nutrisi teh kompos bulu ayam terhadap pertumbuhan pakcoy. serta mengetahui penggunaan teh kompos bulu ayam untuk dapat mengantikan larutan hara konvensional pada sistem hidroponik.Penelitian ini menggunakan Rancangan Acak Lengkap (RAL) faktor tunggal. terdapat 6 taraf perlakuan yang merupakan konsentrasi nutrisi teh kompos bulu ayam yang terdiri dari E0 (1000 ppm Ab-mix). E1 (900 ppm teh kompos). E2 (800 ppm teh kompos). E3 (700 ppm teh kompos). E4 (600 ppm teh kompos). E5 (500 ppm teh kompos) dengan 3 ulangan. Peubah yang diamati yaitu adalah tinggi tanaman. jumlah daun. warna daun. berat basah dan berat kering tanaman. Hasil penelitian menunjukkan bahwa perlakuan nutrisi teh kompos bulu ayam berpengaruh sangat nyata jika dibandingkan dengan Ab-mix yang menunjukan Ab-mix lebih superior terhadap peubah yang diamati. meliputi tinggi tanaman. jumlah daun. warna daun. berat basah dan berat kering tanaman. Namun pada minggu pertama dan kedua pertumbuhan pakcoy masih relatif sama antar perlakuan. Semua perlakuan dengan menggunakan nutrisi teh kompos bulu ayam belum mampu menggantikan nutrisi konvensional.

Lettuce (Lactuca sativa, variety Salanova) production in decoupled aquaponic systems: Same yield and similar quality as in conventional hydroponic systems but drastically reduced greenhouse gas emissions by saving inorganic fertilizer.

Decoupled aquaponic systems have the potential to become one of the most effective sustainable production systems for the combined production of animal protein and plant crops. Here, recirculating aquaculture systems for fish production are combined with hydroponics for soilless plant production thereby recycling dissolved nutrients derived from metabolism of the fish. The aim of the present study was to characterize hydroponic lettuce production using conventional nutrient solution in comparison with decoupled aquaponics using the nutrient rich fish water as basis for the nutrient solution being supplemented by missing nutrients. In addition, one aquaponic treatment became disinfected in order to assess any occurring advantage of the aquaponics derived fish water. For evaluation the temperature, electrical conductivity, pH, and the mineral composition of the nutrient solution, as well as colony forming units in the fish water were monitored. Additionally, plant growth (fresh and dry weight, number and area of leaves) and quality parameters of lettuce leaves (nitrate, mineral content, phenolic compounds) were examined. Carbon sources and microorganisms derived from fish water seem to have neither beneficial nor detrimental effects on plant growth in this study. Except for some differences in the mineral content of the lettuce leaves, all other quality parameters were not significantly different. The use of aquaponic fish water saved 62.8% mineral fertilizer and fully substituted the required water for the nutrient solution in comparison to the control. Additionally, the reduced fertilizer demand using decoupled aquaponics can contribute to reduce greenhouse gas emissions of an annual lettuce production site per ha by 72% due to saving the energy for fertilizer production. This study clearly demonstrates the huge potential of the innovative approach of decoupled aquaponics to foster the transformation of our conventional agriculture towards sustainable production systems saving resources and minimizing emissions.

Comparison of Lactuca sativa growth performance in conventional and RAS-based hydroponic systems

A recent study related to aquaponics has shown that hydroponic lettuce grown in aquaculture-derived supplemented water grew significantly better than lettuce grown in a conventional hydroponic system. The principal objective of this study was to verify this finding in a larger setup. Even though the aquaculture water that was added to the aquaculture-based hydroponic system contained relatively high amounts of sodium, we were still able to observe an enhanced growth performance of the lettuce in that system compared to the lettuce grown in the conventional hydroponic nutrient solution. The lettuce final fresh weight was 7.9%, and its final dry weight even 33.2% higher than the one of the hydroponic control.

Hot Pepper (Capsicum annuum L.) Growth, Fruit Yield, and Quality Using Organic Sources of Nutrients

ABSTRACTMany greenhouse-vegetable growers cannot participate in the organic market due to the scarcity of organic fertilizers, which are able both to (a) satisfy the crop's nutritional needs similarly to when using a nutrient solution, and (b) be regarded as biological, ecological, or in general terms “sustainable.” Four different fertilization regimes using three different hot pepper genotypes were applied under greenhouse conditions in arid land of Mexico. The three genotypes were of the “Serrano” variety and were obtained from different arid lands in northern Mexico. The entire crop management was 100% organic according to United States organic standards. We found that vermicompost—obtained from the metabolism of Eisenia fetida feed with cow manure plus maize waste—was able to supply the needed nutrients to the cultivars to obtain a growth and yield similar to the plants supplied with nutrient solution. The most productive genotype (Don Diego) showed the following fresh yield values: 1.98, 1.84, 1.24, and 1.11 kg plant−1 for treatments with conventional nutrient solution, vermicompost, solarized cow manure, and solarized poultry manure, respectively. The fertilization with poultry manure resulted in lower values in every growth and yield variable measured. However, this same treatment showed the highest values in ascorbic acid with 328.6 and 327.4 mg 100 mL−1 for genotypes Don Ramón and Don Vicente, respectively. The overall results suggest that organic sources of nutrients may be able to supply the needs of greenhouse hot peppers as alternative for organic farmers. Treatment with vermicompost showed the general best behavior in all of the plants.

Calidad biofísica y nutracéutica de frutos de tomate producido con sustratos orgánicos

La creciente inquietud de la opinión pública sobre los efectos negativos de las actividades agrícolas en el ambiente se ha provocado que la producción de cultivos se realice de una manera más sustentable, especialmente en el manejo de la fertilización. Al respecto la composta es un abono orgánico utilizado como fuente de nutrimentos y como componente de sustratos en la agricultura protegida. El objetivo del presente estudio fue evaluar el efecto de diferentes sustratos a base de composta de ganado bovino (C) mezclada con arena de río (A), sobre el rendimiento y la calidad biofísica y nutracéutica de frutos de tomate producidos bajo condiciones en invernadero. Los porcentajes de los sustratos fueron: 25:75, 50:50, 75:25 (C: A) y como control se utilizó la solución nutritiva Steiner en arena. Las variables evaluadas fueron rendimiento, peso promedio de fruto, diámetro polar y ecuatorial, espesor de pericarpio y sólidos solubles totales (calidad biofísica). La calidad nutracéutica se determinó mediante el análisis de licopeno y actividad antioxidante. El mayor rendimiento y calidad biofísica de los frutos se presentó con el uso de la solución nutritiva convencional. En cambio, los frutos obtenidos a partir de composta: arena 75:25 obtuvieron los valores mayores de sólidos solubles y capacidad antioxidante, 12.5 % mayor en sólidos solubles y 27 % mayor en capacidad antioxidante comparados con los obtenidos con solución nutritiva Steiner. La combinación composta con arena para su uso como sustrato orgánico es una alternativa viable para la producción orgánica de tomate en invernadero ya que el rendimiento y la calidad son aceptables. Además; dado el potencial de uso en la agricultura organica certificada, los usuarios eventualmente podrán lograr un sobreprecio y mejorar la relación beneficio/costo, lo que proporciona una potencial comercialización competitiva para el productor, al tiempo que disminuye el uso de insumos inorgánicos con lo que se contribuye a la preservación del medio ambiente.

Response of potatoes to different nutrient solution management in a closed hydroponic system

ABSTRACTIon control of nutrient solutions to control nitrogen (N), phosphorus (P), and potassium (K) was developed for Superior (medium-to-early maturing) and Atlantic (mid-late) potato cultivars grown in closed hydroponic systems in which solutions were replenished and recirculated. Results were compared with conventional nutrient solution management strategies. In the “solution replacement” treatment, nutrient solutions were completely replaced each week. In the “electrical conductivity (EC) control” treatment, water use by potato plants was compensated by adding ground water to achieve the original volume (water replenishment) and the diluted EC of the solution was adjusted to the target levels using stock solution. In “ion control” treatment, ammonium dihydrogen phosphate (NH4H2PO4) and potassium nitrate (KNO3) were added to the EC-controlled nutrient solution. The amounts increased with plant age in both cultivars. The concentrations of nitrate (NO3), P, and K in the ion control nutrient solution could be maintained at target levels. In water replenishment, recycling of nutrient solution resulted in a progressive decrease in EC and an increase in pH. Root activity increased by 93% and 59% in the Superior and Atlantic cultivars, respectively, compared with the nutrient solution replacement. These changes decreased photosynthesis, plant growth, water use, and thus tuber growth in the Superior cultivar. Decreased growth of shoots and tubers occurred without affecting photosynthesis in the Atlantic cultivar. Although there were no significant differences in root activity, photosynthesis, or plant growth between the ion control treatment and the EC control treatment, increased tuber growth was observed in the ion control treatment, possibly as a result of the constant supply of nutrients. High tuber growth and the capability to maintain solution nutrient concentration in the ion control treatment are highly desirable for closed hydroponic systems.

Sweet grape mini tomato grown in culture substrates and effluent with nutrient complementation

The objective of this study was to evaluate production of Sweet Grape mini tomato (Lycopersicum esculentum Mill.) using culture substrates and nutrient solution sewage effluent, applied by drip irrigation (fertigation). The experiment was conducted at the University of Goiás State (UEG-UnUCET), from June to November 2011 in Anápolis-GO, Brazil. The experimental design was a 2 x 3 factorial arrangement in a randomized complete block design with four repetitions. The plots were made by combining two nutrient solutions, effluent supplemented with mineral fertilizers (EcS); conventional nutrient solution (SnC); in addition three cultivation substrates: 60% of fine sand washed + 40% substrate composed by 20% coconut fiber plus 80% pine bark (S1); 20% coconut fiber and 80% pine bark (S2) and natural coconut fiber (S3). Sewage effluent were determined nitrate, calcium, potassium, manganese, total phosphate, total iron, magnesium, chloride, sulphate, boron, zinc and molybdenum. We evaluated average mass and average number of fruits per bunch, total fruit and total yield per plant. Statistical difference absence among tested solutions indicates sewage effluent can be used as an alternative source of nutrients in growing mini tomatoes in hydroponics.

Use of polishing pond effluents to cultivate lettuce (Lactuca sativa) in a hydroponic system.

The sanitary quality and productivity of hydroponic lettuce (Lactuca sativa L.) plants cultivated under greenhouse conditions and treated with effluent from anaerobic reactor + polishing pond followed by physical-chemical treatment was evaluated. Two hydroponic cultivations were performed at summer and winter time at Vitoria-ES, Brazil. The treatments for both cultivations were: T1) conventional nutrient solution, T2) effluent from physical-chemical treatment, T3) effluent from polishing pond, and T4) effluent from polishing pond with 50% dilution. The plants were evaluated for microbial contamination, productivity and nutrient content. In all cases, no significant microbial contamination of lettuce was detected and the levels of macronutrients in the shoot system were similar to those in published reports. In the experiments from summer season, the treatments T1 and T2 resulted in higher production than the T3 and T4 treatments. Plants from T3 and T4 had a less developed root system as a result of reduced oxygenation from competition with the higher algae biomass content from the polishing pond effluent. In the winter season, the effect of the algal biomass was pronounced only in the T3 treatment (undiluted effluent from polishing pond). In conclusion, hydroponic cultivation of lettuce with pond effluent is suitable as a complement to water and nutrients for plants.

An agar nutrient solution technique as a screening tool for tolerance to zinc deficiency and iron toxicity in rice

Studies examining iron (Fe) toxicity and zinc (Zn) deficiency in rice have shown that screening experiments in nutrient solutions are of limited use because the rankings of genotypes as tolerant or intolerant can be very different from the results obtained in field-screening experiments. A possible reason for such deviation is that crucial rhizosphere processes cannot be reproduced in nutrient solutions. The objective of the present study was to evaluate the suitability of low-concentration agar nutrient solutions (ANS) as an alternative screening tool. Agar was dissolved in boiling water and mixed with nutrient solution to achieve a final agar concentration of 0.1% (w/v). Zinc deficiency was induced by supplying Zn at a low concentration (0.1 × 10−3 µmol L−1), while Fe toxicity was induced by supplying excess Fe2+ (200 mg L−1). Three-week-old seedlings were transplanted into this medium. Symptoms of Zn deficiency and Fe toxicity developed more rapidly in ANS compared with conventional nutrient solutions (CNS). For Zn deficiency this was probably because of the development of Zn depletion zones as a result of the reduced convection in the viscous agar medium. In the case of Fe toxicity we observed far less Fe precipitation in ANS compared with CNS. Genotypic comparisons showed that the tolerance rankings obtained in ANS were very similar to the field tolerance rankings, whereas this was not the case in CNS. This was particularly evident with regard to the considerable root growth inhibition detected in intolerant genotypes when stress treatments were imposed in ANS.

Effect of nutrient sources on cucumber production in different substrates

The research was conducted in two successive seasons to compare the effect of nutrient sources, organic manure and inorganic conventional nutrient solution, in cucumber production performed with different local substrates. In fall, the experiment was designed to test three factors, namely cultivar [(a) Armada, (b) Gordion], nutrient source [(a) inorganic nutrient solution, (b) solid organic manure] and substrate [(a) 3 + 1 perlite + clinoptilolite, (b) 1 + 1 perlite + clinoptilolite, (c) 3 + 1 tuff + clinoptilolite, (d) 1 + 1 tuff + clinoptilolite, v/v]. Results showed that organic manuring decrease the total yield by 22.4% in comparison to inorganic nutrient solution. In organic manure treatment, vigorous variety (Armada) gave higher yield than less vigorous variety (Gordion). In the spring season, the tested factors were decreased to two and tested as nutrient source [(a) inorganic nutrient solution, (b) solid organic manure, (c) organic nutrient solution] and substrate. Armada was the only cultivar. Compared to that of the inorganic nutrient solution, total yield was reduced by 10.9% in the organic nutrient solution system and 31.3% in solid organic manure treatment.

Effects of Aluminum Toxicity on Wheat Plants Cultivated Under Conditions of Varying Ionic Strength

The effects of aluminum (Al) toxicity on growth of Triticum aestivum, cv. Atlas 66, were studied under varying conditions of solution electrical conductivity (EC). In solutions containing only 400 μM CaCl2 (low EC) with daily nutrient additions (0.20 g nutrient g plant−1 day−1), severe Al toxicity was observed at 20 μM Al. In more conventional nutrient solutions containing 3600 μM N and all other essential nutrients in optimal proportions (high EC), more than 200 μM Al was required to reduce plant mass production below 50% of control. Solution pH increased in both high and low EC solutions as a result of plant growth, but the effect was counteracted by Al toxicity. In low EC solutions (with daily nutrient additions), EC remained stable with time in the treatments without Al, reflecting a balance between the relative addition rate (RAR) of nutrients and the relative growth rate (RGR) of plants. In the presence of Al, solution EC increased as Al toxicity reduced the RGR of plants below the RAR. In high EC solutions, EC values decreased with time in all treatments as plant growth depleted fixed nutrient stocks. The extent of decline in EC was proportional to plant growth over the experimental period. The results of this study demonstrate that Al is more toxic when solution EC is maintained at low levels using the relative addition rate (RAR) technique. In contrast to high EC treatments, low EC treatments provided a growth response that was more consistent with those observed under field conditions. Use of the RAR technique and low EC conditions should be considered in future experiments.

SILICON.

Silicon is present in plants in amounts equivalent to those of such macronutrient elements as calcium, magnesium, and phosphorus, and in grasses often at higher levels than any other inorganic constituent. Yet except for certain algae, including prominently the diatoms, and the Equisetaceae (horsetails or scouring rushes), it is not considered an essential element for plants. As a result it is routinely omitted from formulations of culture solutions and considered a nonentity in much of plant physiological research. But silicon-deprived plants grown in conventional nutrient solutions to which silicon has not been added are in many ways experimental artifacts. They are often structurally weaker than silicon-replete plants, abnormal in growth, development, viability, and reproduction, more susceptible to such abiotic stresses as metal toxicities, and easier prey to disease organisms and to herbivores ranging from phytophagous insects to mammals. Many of these same conditions afflict plants in silicon-poor soils-and there are such. Taken together, the evidence is overwhelming that silicon should be included among the elements having a major bearing on plant life.

Plant availability of selenite and selenate as influenced by the competing ions phosphate and sulfate

The relative plant availability of selenate versus selenite depends on the concentrations of competing ions, specifically sulfate and phosphate, respectively. In solution culture, the concentration of phosphate is typically 100- to 1000-fold greater than in soil solution, an artifact that could lead to underestimation of the phytoavailability of selenite. A nutrient solution study was conducted to compare the availability of selenite and selenate to perennial ryegrass (Lolium perenne L. cv. Evening Shade) and strawberry clover (Trifolium fragiferrum L. cv. O'Conner) at basal concentrations of SO4 (0.5 mM) and PO4 (2 μM) similar to those found in soil solution. Concentrations up to 5 mM SO4 and 200 μM PO4 allowed quantitative comparison of the efficacy of the competing ions. In both species, selenite was more phytotoxic than selenate, especially for shoot growth. Selenate was less toxic, and tended to preferentially inhibit root growth. Translocation percentages were much higher with selenate (≥84%) than with selenite (≤47%). A 10-fold increase in sulfate decreased uptake from selenate by >90% in both species. In ryegrass, 10-fold increases in phosphate caused 30% to 50% decreases in Se accumulation from selenite, but in clover such decreases only occurred in the roots. Sulfate-selenate antagonisms were thus stronger than phosphate-selenite antagonisms. Nonetheless, conventional nutrient solutions with millimolar phosphate will significantly underestimate Se availability from selenite, and moderate levels of sulfate salinity can inhibit selenate uptake sufficiently to reverse the apparent relative availability of the two forms of Se.

Effect of N concentration and N source on root colonization by Pseudomonas fluorescens 2-79RLI

Wheat (Triticum aestivum L.) was grown in nutrient solution with low or high N supply (NH4NO3 as N source). To further evaluate the influence of N form and its interaction with the nutrient solution pH, wheat plants were grown with NH 4 + or NO 3 - either in an conventional nutrient solution or in a nutrient solution in which the pH was maintained at pH 6.5 using a pH-stat system. The nutrient solution was inoculated with Pseudomonas fluorescens 2-79RLI, a genetically modified bacterium that contains lux genes activated by a ribosomal promoter. Cell numbers and physiological status of P. fluorescens 2-79RLI (length of the lag phase of bioluminescence) in the rhizosphere were determined at the root tip and in the lateral root zone. Nitrogen deficiency decreased both plant growth and root colonization by P. fluorescens 2-79RLI at the root tip while it had no effect on root colonization in the lateral root zone. The physiological status of P. fluorescens 2-79RLI was not affected by nitrogen deficiency. Ammonium nutrition increased root colonization by P. fluorescens 2-79RLI at the root tip and in the lateral root zone when the pH of the nutrient solution was allowed to change according to the N form provided. Under these conditions, the physiological status of P. fluorescens 2-79RLI was higher in the lateral root zone than at the root tip. In contrast, N source had no effect on root colonization or physiological status of P. fluorescens 2-79RLI in the nutrient solution maintained at pH 6.5. It is concluded that the stimulation of root colonization by NH 4 + in the nutrient solution, not maintained at a constant pH, may be due to increased leakage of solutes into the rhizosphere as a result of impaired exudate retention by high H+ concentration in the rhizosphere or the apoplast.

Development of a boron buffered solution culture system for controlled studies of plant boron nutrition

Chelated-buffered nutrient solutions are used for studies on micronutrient metals but so far no equivalent system exists for boron nutrition studies: the present investigation was initiated with that intention. From a literature review, it was noted that a range of substances form chelates with boron including polyhydric alcohols, sugars and phenolic compounds. However, none apart from hydrofluoric acid formed chelates with formation constants comparable to those of micronutrient metal chelates like diethylenetriaminepentaacetic acid (DTPA). Moreover, most chelating substances had deleterious side effects which reduced their possible use in water culture: many of the compounds are substrates for bacterial growth, some are harmful to handle, and others are toxic to plants or humans. Borosilicate glass; was tested in a laboratory experiment but found to release boron too slowly into solution to maintain constant boron concentration in solution even when very finely ground. Current investigations centre around the use of a boron-specific resin, which strongly complexes H3BO3 on its N-methyl glucamine functional groups. The boron sorption capacity of the resin varied from 2.2 to 5.0 mg B g-1 resin. Boron saturated resin maintained an equilibrium solution boron concentration of 46 ut M when added at the rate of 2 g of resin to 1 L of boron free triple deionised water. Plants grown in complete nutrient solution with boron saturated resin added at 1 g per litre of nutrient solution grew as well as plants grown in conventional nutrient solution containing 9.2 ut M boron and their shoots contained adequate boron concentrations for growth. There was no evidence that the resin had effects on plant growth other than in releasing and equilibrating boron concentration in the nutrient solution.